This invention relates to valve trains for overhead valve engines and, in particular, to efficient valve trains for engines having three valves per cylinder.
Internal combustion engines have been provided with numerous types of valve configurations, commonly including two, three or four valves. The valves are configured to obtain desirable gas flow, compression and combustion results while providing simplicity of the valve train to the extent possible for the particular engine arrangement. The most simple valve arrangements have generally involved a single intake valve and a single exhaust valve actuated by an overhead valve train including a single camshaft with cam followers and push rods actuating rocker arms of an overhead valve train. For obtaining higher engine outputs, valve configurations with four valves per cylinder have become common, utilizing dual intake valves on one side of the cylinder, usually the inside and dual exhaust valves on the other, outside, of the cylinder. Such valve configurations are more commonly actuated by multiple overhead camshafts directly driving the valves, or by a single overhead camshaft per cylinder bank driving some of the valves directly and others through finger followers or other rocker mechanisms.
An alternative valve configuration utilizes three valves per cylinder, generally including dual intake valves disposed along an inner side of the cylinder and a single exhaust valve located toward an outer side of the cylinder. Valves of this type may be actuated by overhead camshafts. Alternatively, a single camshaft per engine may connect through cam followers and push rods with rocker arms which actuate the various valves. The valve trains for such cylinder configurations vary in complexity and efficiency as do the valve arrangements themselves, and the relative placement of an igniter such as a spark plug and, if used, a fuel injector for the cylinder.
The present invention provides a valve train layout for an overhead valve (OHV) engine which uses a single camshaft in the cylinder block. A combustion chamber is provided for each cylinder which utilizes two inlet valves and a single exhaust valve. The two inlet valves may, as desired, be of equal or differing diameters. They are longitudinally aligned on the inner side of the cylinder (or combustion chamber) and are symmetrically located on opposite sides of a lateral plane through the cylinder axis and extending normal to the axis of the engine crankshaft and camshaft.
The single exhaust valve may be located either on the lateral plane or asymmetric to one side of the plane, depending on the requirements of the combustion system. Preferably, the exhaust valve is displaced to one side of the lateral plane and along the outer side of the cylinder and is inclined at a compound angle relative to the lower face of the cylinder head and the associated mounting deck of the engine cylinder block.
The inlet valves are preferably actuated by a cam follower and single push rod driving a rocker arm with dual arms carrying separate lash adjusters for actuating the two inlet valves. The exhaust valve is preferably actuated by a cam follower with a lash adjuster driving a single push rod operating a primary, or slave, rocker arm which in turn drives a secondary push rod actuating an exhaust rocker arm that opens the exhaust valve. Conventional springs are provided to close the valves and maintain the cam followers in contact with their cams.
In one embodiment, the primary or slave rocker arm for the exhaust valve is pivotable on a common axis with the intake rocker arm. In an alternative embodiment, the primary or slave rocker arm is pivotable on a canted pivot axis. In each case, a secondary push rod drives an exhaust rocker arm pivotable on a canted axis to engage the exhaust valve while pivoting in a plane common to the valve axis. In either embodiment, the camshaft may if desired be controlled by a cam phaser for varying valve timing.
Both embodiments for an overhead valve engine provide improved inlet port flow for better specific power output and dynamic range through the use of the two inlet valves. Improved exhaust port flow is obtained due to the compound angle of the exhaust valve. Better catalytic converter performance is obtained due to the reduced heat loss compared to a system with two or more exhaust valves. The compound angle of the exhaust valve also permits a larger exhaust valve for a given cylinder bore size. The space occupied by of the upper portion of the engine is reduced significantly over a multi-valve engine with overhead camshafts.
Hydraulic lash adjusters may be provided for all three valves in the engine layout although mechanical lash adjustment could be used if desired. With a camshaft phaser, the inlet and exhaust timing may be adjusted for better performance. A potential for reduced hydrocarbon emissions is possible due to reduced crevice volume associated with the single exhaust valve as opposed to dual exhaust valves in four-valve engines. The invention provides valve train driving inlet and exhaust valves on substantially different axes without using common rocker shafts that have longer, less desirable, rocker arm arrangements. Finally, a simple cam drive for a multi-valve engine cylinder concept is provided which allows improved cylinder head water jacket geometries and better cylinder head cooling performance.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.